The present invention relates to a hydrogen storage alloy used as a negative electrode of a nickel-hydrogen cell, and particularly to a hydrogen storage alloy which has attained a low cost by suppressing the Co-content as well as providing a long life.
The hydrogen storage alloy fall into type AB, comprising rare earth elements and nickel (Ni), type AB.sub.2 comprising zirconium (Zr) and manganese (Mg), and the like. Among these, type AB.sub.5 is mainly used as a negative electrode material for nickel-hydrogen cells mounted in portable equipment and the like.
In nickel-hydrogen cells, it is known to use alloys consisting of rare earth elements and nickel containing ternary or quaternary compositions such as RNiAlCo, RNiMnAlco and LaNiMnAlCo. In practice, in nickel-hydrogen cells, the hydrogen stored alloys usually contain about 6.about.10 wt. % Co.
The reason for adding Co element to the above-mentioned alloys is to improve the cycle life of charge and discharge.